The study was able to capitalize on comprehensive information from national databases and registries. Investigators drew from a national histopathology and cytopathology registry as well as from a national vital statistics database. A comprehensive cancer database was used to establish both reference incidence values for males and females and the number of expected cases within the study group.
In both transgender men and women, exactly 50% of cases were ductal carcinoma, compared to 85% in the group of reference women.
An additional 31% of the breast cancers in transgender women were lobular, 6% were ductal carcinoma in situ (DCIS), and the remainder were of other types. Of the cancers in transgender women, 82% were estrogen receptor positive, 64% were progesterone receptor positive, and 9% were Her2/neu positive.
For transgender men, there were no lobular carcinomas; 25% were DCIS, and 25% were of other types. Half of the cancers were estrogen receptor positive, and half were progesterone receptor positive; 25% were Her2/neu positive, and there was one case of androgen receptor positive breast cancer.